1. Field of the Invention
The present invention relates to a transformer provided with an amorphous core and a plurality of coils in which the amorphous core is inserted, and more particularly, to a coil structure thereof.
2. Description of the Related Art
Transformers are generally known to vibrate by an electromagnetic mechanical force at the time of short circuit in such a way that an inner coil and an outer coil of their own coil repel each other. As such effects, for example, a bobbin may be buckled to the inside or a gap may be produced between the inner coil and the outer coil. Thus, occurrence of fluctuation, displacement or the like as effects of the electromagnetic mechanical force on the coil is pointed out as problems with transformers. Furthermore, in the case of a three-phase coil or the like, this coil vibration varies with time due to a phase difference (e.g., 120 degrees) between coils, and therefore the coils are known to influence each other. The time difference or phase difference in vibration between the coils causes an unpredicted force to be applied to windings of the coils and it is necessary to consider effects of the unpredicted force on the transformer itself.
Japanese Patent Laid-Open Publication No. 10-340815 (Patent Document 1) describes a related art in this technical field. Referring to an amorphous core transformer provided with an amorphous core wound with amorphous thin magnetic ribbons in multiple layers and a plurality of coils, this document points out as problems to be solved how to secure buckling strength for an inner coil and an outer coil that constitute the coil, how not to press the amorphous core and how not to deteriorate iron loss or excitation current. As a solution, the document discloses that a coil drum made up of a plurality of drum members arranged in a width direction of the core member is provided on the innermost circumference of at least one coil and the outermost amorphous core includes a strengthened frame that surrounds the core and presses the outside of the coil in which the core is inserted.
Another related art is Japanese Patent Laid-Open Publication No. 2010-118384 (Patent Document 2). The art described in this document provides a coil drum for a transformer and a transformer using the same that have as an object to secure buckling strength of an inner winding of a coil of the transformer and prevent pressure on its core, and do not deteriorate iron loss or excitation current. As a solution, the core is made up of a wound core which is wound with magnetic ribbons in multiple layers or cores stacked in multiple layers and the coil is inserted in the core. The coil drum arranged on the innermost circumference of the coil is formed into an arc shape outside, thus improving strength against buckling recessed toward the inside which is the core side. Therefore, the document describes that buckling strength with respect to the inner winding is secured, and the core is never pressed or iron loss or excitation current does not deteriorate either even in the case of a large-volume transformer.
A further related art is Japanese Utility Model Laid-Open Publication No. 54-126015 (Patent Document 3). This document relates to a static induction electric apparatus, and more particularly, to a core of a transformer or reactor and a winding tightening device. As a solution, the document describes a core of a transformer and a winding tightening device for a static induction electric apparatus including a core and a winding wound around the core together with an insulating medium accommodated in a tank, wherein a high strength inter-phase insulating member inserted between phases of windings and a seat provided on a tightening metal that sandwiches the insulating member and a core yoke are engaged with each other and secured via a tightening member to thereby tighten the core yoke and the winding together.
A still further related art is Japanese Patent Laid-Open Publication No. 55-16419 (Patent Document 4). This document relates to a core-type transformer including, for example, a winding having a square cross section. As a solution, the document describes a core-type transformer including a core, a winding wound around the core and an external box that accommodates a winding section, wherein the periphery of the winding is supported by the external box via an insulating section.
A still further related art is Japanese Utility Model Laid-Open Publication No. 3-3719 (Patent Document 5). This document relates to an electromagnetic inductive winding structure used for a transformer or other electromagnetic inductive apparatuses. As a solution, the document describes an electromagnetic inductive apparatus in which outer circumferences of windings of different phases arranged in parallel via an inter-phase spacer are collectively secured using an insulating fixing band.
Furthermore, a still further related art is Japanese Patent Laid-Open Publication No. 8-222458 (Patent Document 6). This document relates to a reactor, transformer or the like designed to reduce noise and/or vibration and reduce the size and/or weight. As a solution, the document describes a reactor transformer including a core and a plurality of coils, wherein the core and the coils are fixed together, and further the coils are fixed together so as to suppress vibration of the core.
Furthermore, a still further related art is Utility Model Registration Publication No. 3063645 (Patent Document 7). This document relates to provision of a central body fixing structure of a transformer that reduces damage of an amorphous core. As a solution, the document describes a central body fixing structure of a transformer in which insulating piece/insulating plate structures are provided at a top end and a bottom end inside a coil, the insulating plates are arranged so as to interlace with each other, cover an outer edge of the amorphous core in a ring shape and protrude relatively high, the insulating plates are sandwiched between the coil and a case so that the amorphous core wound with the coil is also indirectly positioned therein without requiring any holding force of the coil and the case to fix the amorphous core and thus preventing damage to the amorphous core.
Transformers are apparatuses that convert high-voltage and low-current AC power to low-voltage and high-current AC power or vice versa, and are provided with a core that constitutes a magnetic circuit and a coil that constitutes an electric circuit. FIG. 9(A) shows a cross-sectional view of a coil 803 of a conventional amorphous core transformer. When manufacturing a transformer using an amorphous core 802, since amorphous ribbons are very thin and difficult to mold, it is a general practice that amorphous ribbons of the same width are stacked on one another in a core shape. For this reason, the cross-sectional shape of the amorphous core 802 is a substantially rectangular shape, and since a rectangular bobbin 805 is used accordingly, gaps 810 are produced in rectilinear parts between an inner coil 807 and the rectangular bobbin 805 during a winding operation. Thus, the coil size becomes greater than its design value, making assembly impossible, or in a short circuit test conducted after completion of assembly of the transformer, an electromagnetic mechanical force produced at the time of short circuit causes repulsion between the inner coil 807 and an outer coil 808, an electric wire drops into the gaps 810 between the inner coil 807 and the rectangular bobbin 805, thus producing gaps 811 between the inner coil 807 and the outer coil 808 and increasing short circuit impedance (FIG. 9(B)).
Pressing the amorphous core and imposing load on the amorphous core deteriorate no load loss. This may cause transformers to fail to satisfy their standard values and fail to pass a model test or the like. Due to these problems, it is particularly difficult to manufacture a large-volume model whose electromagnetic mechanical force increases at the time of short circuit. The electromagnetic mechanical force of a coil refers to a force acting in accordance with the law that different electric wires through which currents pass in the same direction at the time of short circuit attract each other and electric wires through which currents pass in opposite directions repel each other.
The related arts provide a press process to reduce these gaps and determine the size of the coil, which may result in an increase in the amount of man-hours. Furthermore, there is a method for reducing the gaps by strongly winding electric wires, but strongly winding electric wires may destroy insulating coating of the electric wires in the corners of the rectangular bobbin. Thus, the present invention provides an amorphous core transformer in a simple configuration provided with a coil with reduced gaps between electric wires and a bobbin of the coil.
Regarding such a transformer, for a core transformer that uses a silicon steel plate or amorphous magnetic material as the material of the core and uses a wound core as the core structure, the above-described patent documents already disclose a technique of preventing the coil from deforming through buckling and pressing the wound core. The technique for such a core transformer disclosed in these patent documents is a measure taken for buckling of the coil itself and the patent documents give no description of the fact that the coils influence each other when there are a plurality of coils like a three-phase transformer and the coils vibrate due to an electromagnetic mechanical force at the time of short circuit.
However, in the case of a three-phase coil or the like, since there is a phase difference (e.g., 120 degrees) between coils, vibration of the coils also varies with time, and the coils are thus known to influence each other. It is therefore necessary to take into consideration the influences of an unpredicted force being applied to the windings of the coils due to the time difference or phase difference of vibration among the coils and an unpredicted force also being applied to the transformer itself. For example, neighboring coils normally function as stoppers to suppress displacement toward the outside of the coil, but the time difference of vibration eliminates the function and a gap may be produced between the inner coil and the outer coil. There is a problem that fluctuation, displacement or the like occurs as a result of the electromagnetic mechanical force applying to the coils.
The present invention has been implemented in view of the above-described problems and it is an object of the present invention to provide a transformer capable of effectively suppressing fluctuation, displacement or the like of coils caused by an electromagnetic mechanical force or the like.